FIG. 29 shows a prior art example of a mold apparatus for resin encapsulation of an electronic component such as a semiconductor device. The apparatus comprises: an upper mold set 1 involving an upper chase 2; and a lower mold set 3 involving a lower chase 4. The lower mold set 3 is pushed up, whereby this lower mold set 3 is pressed and clamped against the upper mold set 1. A substrate board 7 is thereby sustained between cavity bars 5 installed in the lower surface of the upper chase 2 and cavity bars 6 installed in the upper surface of the lower chase 4. Then, a plunger 3a is ejected by a driving mechanism which is not shown in the figure, whereby a solid tablet 8 in a pot 3b undergoes a heating compression to fluidity, and whereby an electronic component (not shown) mounted on the surface of said substrate board 7 is encapsulated with resin. In said mold apparatus, the variation (maximum 0.02 mm) of thickness among metallic substrate boards 7, such as lead frames, has been compensated by the elastic deformation of elastic pins 2a in the axial direction. Further, numeral 9 designates a support block constituting said lower mold set 3.
However, the needs for resin encapsulation of plastic substrate boards, such as so-called substrates, have been growing in recent years. The variation (maximum 0.2 mm) of thickness among plastic substrate boards is generally much larger than that among metallic substrate boards. Such variation of board thickness is difficult to be compensated completely by said elastic pins 2a having a small capacity for elastic deformation. Therefore, a gap is unavoidable to occur, thereby causing a flash frequently. In addition to this incapability, the increase of the displacement causes said elastic pins 2a easily to fatigue failure, thereby requiring an early-stage change, thereby increasing the maintenance work. Further, in the above-mentioned example of the prior art, the elastic pins 2a need a change depending on the substrate board to encapsulate with resin because of the small capacity of the elastic pins 2a for elastic deformation. The change takes a lot of troubles during disassembling and reassembling the mold apparatus. Thus, a method has been proposed to use overlaying such as plural conical belleville springs (not shown) having a larger capacity for elastic deformation than said elastic pins 2a. However, said conical belleville springs have a problem of variation in spring force (recoiling force) and a further problem that the spring force (recoiling force) changes due to the heating compression strokes.
Considering said problems, a first object of the present invention is to provide a mold apparatus for resin encapsulation, which is capable of compensating completely a large variation of thickness mainly among plastic substrate boards, thereby avoiding the occurrence of a flash, and is easy of maintenance.
On the other hand, a mold-clamping force corresponding to the resin encapsulation of a plastic substrate board is insufficient as the mold-clamping force for the resin encapsulation of a metallic substrate board (lead frame and the like). Thus, the metallic substrate board cannot be encapsulated with resin.
For the information, a mold-clamping force of about 1–5 kg/mm2 is sufficient for a plastic substrate board, which can be generated by a small oil hydraulic cylinder capable of being built in the mold apparatus. In contrast, with regard to the mold-clamping force for metallic substrate boards, a copper lead frame needs a mold-clamping force of 20–30 kg/mm2, and a steal lead frame needs a mold-clamping force of 25–40 kg/mm2. Thus, a large mechanism for oil pressure generation is necessary if used, as well as a large cylinder and the like. Therefore, overall system becomes so large as not to be built in the mold apparatus. On the contrary, if a plastic substrate board is applied with a mold-clamping force of the same order as that for a metallic substrate board, the plastic substrate board deforms and eventually breaks in a worst case.
As such, a plastic substrate board and a metallic substrate board cannot be encapsulated by common mold sets, and each substrate board requires exclusive mold sets and chases. Thus, there have been a problem of increased cost and a problem of a lot of time necessary for the change thereof.
Considering said problems, a second object of the present invention is to provide a mold apparatus for resin encapsulation, capable of processing not only a plastic substrate board but also a metallic substrate board.
Further, when a plastic substrate board is clamped indiscriminately with a strong clamping force, the plastic substrate board is easily deformed, and hence, assembled components, such as semiconductor devices and especially wires, are easily damaged. On the contrary, when said substrate board is clamped indiscriminately with so weak a clamping force as not to cause a deformation, a gap occurs between the substrate board and the mold, causing a problem of the unavoidable occurrence of a flash.
A third object of the present invention is to provide a method of resin encapsulation and a mold apparatus for resin encapsulation, capable of simultaneously resolving the two problems of the damage to an mounted component and of the occurrence of a flash.